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Environmental fate & pathways

Hydrolysis

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Endpoint:
hydrolysis
Data waiving:
study scientifically not necessary / other information available
Justification for data waiving:
other:
Justification for type of information:
In accordance with Regulation (EC) No. 1907/2006, Annex XI, section 1.1.2 Use of existing data, testing does not appear be scientifically necessary as a conclusion from a) data on environmental properties from experiments not carried out according to GLP or the test methods referred to in Article 13(3) and b) available environmental assessments carried out by national authorities published in literature:

A literature search has been performed searching for information in relation to hydrolysis of ethylenediaminetetraacetic acid (EDTA, EC No. 200-449-4; CAS No. 60-00-4) and its metal complexes. As a result of this search some studies were found to be qualified to address the hydrolytic stability of EDTA and its metal complexes.
1. Qualified studies:
The following publications present information about the reaction of the EDTA with water or other chemicals but under non-environmentally representative conditions.
According to several published scientific studies and to the EU Risk Assessment Reports on EDTA and tetrasodium EDTA (EU, 2004a and b; Hirzel, 1996), aminopolycarboxylic acids such as EDTA are resistant to hydrolysis, neither strong acids nor alkalis causing any degradation under natural conditions and ambient temperature. EDTA is not expected to undergo hydrolysis as it does not possess functional groups that hydrolyze under environmentally relevant conditions. The hydrolysis of EDTA occurs only in modified conditions. Since important applications of EDTA involve its use in aqueous solution at high temperature and pressure, hydrolysis of EDTA was studied at elevated temperatures and presence of ammonia by Motekaitis et al. (1979) as well as Palmer and Nguyen-Trung (1994). The hydrolysis and ammonolysis of EDTA were studied in aqueous solution over a range of temperatures and at various pH values with NMR, GC, and GC-MS measurements (Motekaitis, 1979). At high pH in the presence of ammonia, both ammonolysis and hydrolysis occur. In the absence of ammonia, only the normal water-cleaved EDTA hydrolysis products were identified: iminodiacetic acid (IDA) and N-(2-hydroxyethyl)-iminodiacetic acid (HEIDA). The first-order rate hydrolysis constant of EDTA at 175°C was found to be 4.2 x 10-5 s. The value of ΔH0 for this reaction is approximately 35 kcal/mol. Although Palmer (1994) refers to the hydrolytic degradation of the EDTA molecule based on Motekaitis (1979), the study itself is related to the temperature dependence of the pKa's, so the acidity constants of EDTA, even though these are called stepwise hydrolysis quotients in this reference. Palmer claims that the data are useful for studying the kinetics of thermal decomposition of (poly)carboxylic acids. It is mentioned that, although drifting cell potentials at 150°C were indicative of decomposition, no attempt was made to monitor this reaction. Palmer (1994) gives thereby an indication that hydrolysis only becomes noticeable at 150°C (non-environmental conditions).
2. Disqualified studies:
In literature there are other several references with both keywords hydrolysis and (metal-)chelates, but these are in most cases focusing on the reaction of the metal-ion with water (Coutney (1959), Handshaw (1988),) and Wilkins (1969)) and not on the reaction of the chelate with water. The following studies are therefore disqualified for describing the hydrolysis of chelates in water. The hydrolysis of the Fe compound in ferrous EDTA chelates has been dealt in published studies (Wilkins, 1969 and Handshaw, 1988). Both HEDTA and EDTA form complexes with ions. Therefore, both exist naturally as a mixture of chelate complexes. In the study by Wilkins (1969), a temperature – jump relaxation method was used for Fe(III)-EDTA complexes at different pH (6.0 – 9.3). The authors observed precipitation of iron(III) hydroxide or further base hydrolysis to dihydroxy mononuclear complexes at the higher pH. In the study by Handshaw (1988), potentiometric equilibrium pH measurements of 1:1 Fe2+-EDTA and Fe2+-HEDTA solutions with rigorous exclusion of oxygen gave pH profiles showing no indication of hydrolysis up to pH 12. Calculation of the equilibrium constants of these systems gave only the formation constants of the simple 1:1 chelates and constants for the formation of monoprotonated species at low pH. The iron chelate EDTA complex was also investigated by Courtney (1959). The hydrolysis of the Fe(III)-EDTA chelate involves two steps with pK values at 7.5 and 9.4. The formation of the mono- and dihydroxo iron EDTA chelates must involve an opening of a chelate ring in each case.
In conclusion, the presented literature data supports the lack of hydrolysis of EDTA under environmentally relevant conditions. Based on this data and the fact that biodegradation is the relevant degradation pathway of EDTA and its salts in the environment (see chapter 5.2), no additional hydrolysis study according to OECD guideline 111 is considered to be needed, since no relevant new information are expected.

Description of key information

Hydrolysis is not expected to be a relevant degradation pathway.

Key value for chemical safety assessment

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